Various contrivances are made to a rocking chair whose backrest tilts backwards in order to enhance amenity and a degree of satisfaction acquired in a rocking state. Patent Document 1 discloses, as one of such contrivances, a chair whose backrest lowers while tilting backwards and whose seat moves forwards while wholly tilting backwards when a seated person reclines against the backrest.
Forward movement of the seat resultant from rocking action contributes to yielding an advantage of making it easy to perform body stretching even at a small backward tilt angle of the backrest. For this reason, when compared with a case where only the backrest tilts backwards, a resting function per unit backward tilt angle can be enhanced (namely, a high comfortable state can be assured even when the chair is rocked through a small angle).
In Patent Document 1, the backrest tilts backwards while its lower end is moving forwards. In this tilted mode, an upper body of a seated person does not greatly bend backwards when rocking the chair. Accordingly, even when the seated person rocks the chair during operation of a keyboard or a mouse on a desk while viewing a monitor (a display) as in the case of; for instance, operation of a personal computer, the body is not much pulled away from the desk. Consequently, the user can continually perform working in a comfortable state while rocking the chair.
In Patent Document 1, a rear end of the seat becomes lower in a state of forward movement while the height of a front end of the seat remains unchanged, whereby the seat remains backwardly tilted as a whole. As a result of the seat tilting backwards, even when the backrest is lowered, a distance between a lower end of the backrest and a rear end of the seat substantially remains unchanged, so that no relative slippage exists between the backrest and the back of the seated person. As a consequence, it is understood that occurrence of a “curling-up-of-a-shirt” phenomenon in which vertical slippage occurs between a shirt of a seated person and the back thereof can be prevented during rocking.
Patent Document 2 also discloses a chair similar to that described in connection with Patent Document 1. A seat is first described in connection with Patent Document 2. A seat base 102 is fitted to a base (a chassis body) 30, which is fastened to an upper end of a leg (a gas cylinder), so as to be slidable in backward and forward. A seat 18 is attached to the seat base 102. A joint member (a channel member) 136 standing upright behind a backrest 20 is fastened to a rear end of the sheet base 102. A lower portion of the backrest 20 is joined to the joint member 136 by way of a bracket 130 so as to be vertically slidable.
Moreover, a back support bar 104 standing upright behind the backrest 20 and the joint member 136 is fastened to the base 30. Thus, an upper end of the back support bar 104 and a back face of the backrest 20 are slidably joined together. According to Patent Document 2, when a seated person leans against the backrest 20, the backrest 20 in its entirety descends while remaining tilted around the upper end of the back support bar 104. Moreover, the seat 18 moves forwards in synchronism with descending action of the backrest 20.
A plurality of chairs whose seats move backwards when used as rocking chairs have already been put into practice. There are large numbers of documents, including Patent Document 3, in relation to the chairs. In many chairs, a backrest has a back shell (a back panel) made of resin. Disclosed in Patent Document 3 is, as means for attaching the back shell to a backrest frame positioned behind the back shell, to join a lower portion of the backrest to the backrest frame by means of right and left horizontal pins and to join an upper end of the backrest to a back frame in a slidable manner.